Material flow systems should, as far as possible, reach their optimum throughput of the goods to be transported. For this purpose, material flow decisions such as the settings of points or whether new transported goods are to be loaded must be made such that unbalanced loads and jams do not arise. For this purpose, the current load state of the installation and, if present, information on the transported goods planned to be loaded can be used for a prediction of regions of the installation where jams, etc., can be expected. These can then be counteracted with suitable control strategies.
In systems with a central material flow computer (MFC), the computer administers the current loading state centrally and can therefore also calculate a prediction of future states centrally. Given the presence of a plan concerning existing transported goods to be loaded, said plan can also be taken into account for the calculation. Conventional central material flow systems have a central device, the material flow computer, which periodically receives all the necessary information as set out above from the subordinate control devices and can thus predict the future loading. The US patent application US2007/0078531A1 discloses a system and a method for dynamic simulation of process flows, wherein a central “simulation engine” is used. Central material flow computers (MFC) represent a bottleneck which can influence the performance and throughput of the material flow system. Should the central material flow computer fail, the whole material flow system can no longer adapt to changed loading conditions.
In the literature, proposals exist for decentralized material flow systems. Decentralized material flow systems can introduce a central device as an information hub (e.g. passively with an electronic blackboard or actively, similarly to a conventional MFC). But this means that the advantages of a centralized concept (no central bottleneck for performance, no single point of failure, common borders between mechatronics and control system) are lost again. A. Fay and I. Fischer propose in their article “Dezentrale Automatisierungsstrategien für Gepäckfördersysteme” [Decentralized automation strategies for luggage conveying systems] in Automatisierungstechnik 52 (2004) 7, published by Oldenbourg Verlag, for material flow systems to use internet routing mechanisms. However, the proposed decentralized concepts are inflexible and not efficient. For example, no updating is carried out in the case of route changes.
In “Evaluation of Routing Strategies for Decentralized Self-Organization in Large Scale Convey Systems. Progress in Material Handling Research: 2008; Material Handling Institute, 160-184, 2008”, G. Follert and M. Roidl propose a concept without a central element. This is achieved by flooding the system with messages. The communication load produced is very large, since for each transport unit that is loaded, determination of the route is performed by flooding the communication network of the installation.